Anisotropic etch method

ABSTRACT

A method to anisotropically etch an oxide/silicide/poly sandwich structure on a silicon wafer substrate in situ, that is, using a single parallel plate plasma reactor chamber and a single inert cathode, with a variable gap between cathode and anode. This method has an oxide etch step and a silicide/poly etch step. The fully etched sandwich structure has a vertical profile at or near 90° from horizontal, with no bowing or notching.

This is a continuation of Ser. No. 08/194,134, filed Feb. 8, 1994 (nowabandoned); which is a continuation of Ser. No. 07/877,435, filed Apr.30, 1992 (now abandoned); which is a division of Ser. No. 07/574,578,filed Aug. 27, 1990 (now U.S. Pat. No. 5,201,993); which is acontinuation of Ser. No. 07/382,403, filed Jul. 20, 1989 (now U.S. Pat.No. 5,271,799).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to etching methods used in the fabricationof integrated electronic circuits on a semiconductor substrate such assilicon, particularly a single-chamber/single-cathode (in situ) methodof anisotropically plasma etching a sandwich structure of an oxide,tungsten silicide, and polycrystalline silicon, or equivalent structure.

An electronic circuit is chemically and physically integrated into asubstrate such as a silicon wafer by patterning regions in thesubstrate, and by patterning layers on the substrate. These regions andlayers can be conductive, for conductor and resistor fabrication, orinsulative, for insulator and capacitor fabrication. They can also be ofdiffering conductivity types, which is essential for transistor anddiode fabrication. Degrees of resistance, capacitance, and conductivityare controllable, as are the physical dimensions and locations of thepatterned regions and layers, making circuit integration possible.Fabrication can be quite complex and time consuming, and thereforeexpensive. It is thus a continuing quest of those in the semiconductorfabrication business to reduce fabrication times and costs of suchdevices in order to increase profits. Any simplified processing step orcombination of processes at a single step becomes a competitiveadvantage.

2. Description of the Related Art

A situation where a process simplification is desirable is in theanisotropic etch of a layer of oxide on a layer of silicide on a layerof poly (also called an oxide/silicide/poly sandwich structure). In thisdisclosure, "oxide" denotes an oxide of silicon, "silicide", and othercommonly known silicides such as tungsten silicide, tantalum silicide,molybedenum silicide, and titanium silicide is short for tungstensilicide, and "poly" is shoptalk for polycrystalline silicon. "Polycide"denotes a silicide-over-poly combination. Oxide is an insulator withdielectric properties. Poly is resistive in nature, but is made lessresistive when doped with an element having less or more than fourvalence electrons, or when layered with conductive silicide.

An oxide/silicide/poly sandwich structure presents a difficult etchingtask, particularly with an additional mask layer of photoresist("resist"), which must be the case if patterning is desired. Thedifficulty is due to the distinct differences in the way oxide andpolycide are etched, particularly with resist still present on top ofthe structure.

Both oxide and polycide can be etched using a parallel plate plasmareactor. However, an oxide is typically etched in fluorine deficientfluorocarbon based plasmas, whereas silicide and poly can be etched influorine or chlorine based discharges. Reactor cathode materials mayalso differ: for oxide etch, an erodible cathode such as graphite orsilicon is often used to provide a source of carbon or silicon for etchselectivity, whereas for polycide etch, an inert cathode is preferred,especially when utilizing chlorine gas (Cl₂) for selectivity. If asingle-chamber process were attempted using conventional art to etch anoxide/silicide/poly sandwich structure, the erodible cathode requiredfor oxide etch would be destroyed by the chlorine required for polycideetch. Using conventional methods, the two steps are incompatible.

Oxide etch in general is fairly well understood, given a universal needfor a vertical profile. This vertical profile is realized primarily byion induced reaction with the oxide, coupled with normal incidence ofthe ions onto the oxide surface. The amount and energy of these ions areprimarily controlled by the reactor's rf power and gap. Generally, afluorocarbon-based gas mixture is introduced at a low pressure into theetch chamber. The exact gas composition is chosen, and an erodiblecathode is used to scavenge excessive fluorine radicals so that thefluorine-to-carbon ratio is near, but not beyond, the so-calledpolymerization point. Under these conditions, when a plasma is ignited,the fluorocarbons are dissociated and release fluorine radicals andCF_(X) species. Although fluorine radicals etch oxide, they do so veryslowly: the primary etchant for oxide is considered to be the CF_(X)species. Some of these species diffuse to the oxide surface where, withthe assistance of ion bombardment, they react with the oxide and releasevolatile byproducts SiF₄, CO, and CO₂. In addition, some of the CF_(X)species react with each other to form fluorocarbon polymers. Polymerthat forms on horizontal surfaces is removed by vertical ionbombardment. Polymer that forms on vertical sidewalls is notsignificantly degraded by the bombardment, and actually serves a usefulpurpose by protecting the sidewalls from attack by the etchant species.This sidewall protection enables the achievement of vertical profiles,adjustable by varying the fluorine-to-carbon ratio. As the cathode iseroded, the quantity of available fluorine radicals is reduced.Therefore, a polymer-producing gas such as CHF₃ is balanced against afluorine-producing gas such as CF₄ to provide proper selectivity, withassistance to sidewall protection.

Two methods are presently used to etch an oxide/silicide/poly sandwichstructure. Both methods use separate reactors: one for oxide etch andone for polycide etch. The first method involves etching the oxide in anoxide etch reactor, using an erodible cathode. After oxide etch, theresist is removed from the wafer. Silicide and poly are then etched in apoly etch reactor, using an inert cathode. Both etches are anisotropic.

The second method uses the same principles as the first, except thatthere are two reactors in one machine. The two reactors are configuredas separate oxide and polycide reactors having a common vacuum transferarea, so that a wafer can be transferred in a vacuum from the oxidereactor to the polycide reactor, thus minimizing additional handling.The resist is generally not removed prior to polycide etch in thismethod. This is sometimes referred to as "in situ" since the wafersnever leave the vacuum of one machine. However, they are etched in twodifferent etch chambers and are not truly in situ in the sense of thisdisclosure.

It would be of great advantage to etch oxide and polycide truly "insitu", that is, in one reactor chamber, with a single cathode.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method ofanisotropically etching an oxide/silicide/poly sandwich structure insitu. Other objects of the invention are a fast processing time andimproved process yield and cleanliness.

In summary, the inventive process is as follows. A wafer having thesandwich structure described above, coated with a mask layer of resist,is transferred into the chamber of a parallel plate plasma reactor,having an anodized aluminum cathode and a variable gap, for two steps:oxide etch and polycide etch. In the oxide etch step, oxide notprotected by resist is exposed to a plasma of about 1.9 W/cm² powerdensity at a 0.48 cm gap, in a 2.3 torr atmosphere of 50 sccm C₂ F₆, 100sccm He, 40 sccm CF₄, and 32 sccm CHF₃. Immediately after the oxide etchstep, in the same chamber and using the same cathode, silicide and polylayers are etched in a plasma of about 0.57 W/cm² at a 1.0 cm gap in a0.325 torr atmosphere of 90 sccm Cl₂ and 70 sccm He. The finishedstructure has a vertical profile at or near 90° from horizontal, with nobowing or notching. The entire inventive process takes about 3 minutes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectioned oxide/silicide/poly sandwich structurewith a patterned resist mask layer, prior to the inventive etch.

FIG. 2 shows a cross-section of said structure after oxide etch.

FIG. 3 shows a cross-section of said structure after polycide etch.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As illustrated in FIG. 1, a photoresist mask layer 10 is aligned anddeveloped on a sandwich structure of oxide 11, silicide 12, and poly 13on gate oxide 14 of a silicon wafer substrate 15. Fabrication andmasking of this structure are done by methods well known to thoseskilled in semiconductor design and processing, and hence are not fullydisclosed herein. The preferred embodiment of the inventive method iswell suited to etch a 3,000 angstrom layer 11 of TEOS oxide (an oxide ofsilicon, derived from tetraethylorthosilicate) on 1,200 angstroms oftungsten silicide 12 on 3,000 angstroms of poly 13.

The wafer having the masked structure is transferred into the chamber ofa Lam 790 parallel plate plasma reactor, having an anodized aluminumcathode, a variable gap, and a 13.56 MHz rf power plasma generator foran inventive process having two steps: oxide etch and polycide etch. Inthe oxide etch step, oxide 11 not protected by resist 10 is exposed to aplasma of about 1.9 W/cm² power density at a 0.48 cm gap, in a 2.3 torratmosphere of 50 sccm C₂ F₆, 100 sccm He, 40 sccm CF₄, and 32 sccm CHF₃.In this disclosure, "sccm" denotes standard cubic centimeters perminute, and "gap" refers to the distance between plasma electrodes, oneof which supports the wafer. After the oxide etch step, which takesunder a minute, the structure appears as shown in FIG. 2.

Immediately after the oxide etch step, in the same chamber and using thesame cathode, silicide and poly layers 12 and 13 are etched in a plasmaof about 0.57 W/cm² at a 1.0 cm gap in a 0.325 torr atmosphere of 90sccm Cl₂ and 70 sccm He. This etch takes a little over 2 minutes, withthe entire inventive process taking about 3 minutes. The finishedstructure appears as shown in FIG. 3, with a profile at or near 90° fromhorizontal, with no bowing or notching.

Details of the oxide etch step are now provided. Although preferredparameter values are stated above, plasma power density can range withinabout 0.18-4.0 W/cm², the gap can vary within about 0.3-0.6 cm,0.38-0.52 cm being the preferred range, and the pressure can rangewithin about 1.8-3.0 torr, although 2.2-2.4 torr is preferred. Gasquantities may vary, as long as at least about 5 sccm He is provided.Providing more CF₄ than CHF₃ makes a cleaner process, but this ratio canbe varied if desired.

The inventive process uses a non-erodible anodized aluminum cathode,which increases the amount of available fluorine radicals. According toconventional thought, in order to maintain the same oxide-to-polycideselectivity as the prior art, the ratio of CF₄ to CHF₃ must be decreasedto minimize fluorine radicals. It was found that this approach does notprovide adequate selectivity without an excessive and quick buildup ofpolymer. This was solved by adding C₂ F₆ to the chamber atmosphere asthe predominant gas, which provides more CF_(X) species and relativelyfew fluorine radicals, resulting in acceptable selectivity withoutexcessive polymer buildup. C₂ F₆ also resolves a "micromasking" problem,in which areas of underlying polycide were not being etched. Althoughthe cause is unclear, it is speculated that the CF_(X) species reactedwith the tungsten silicide, forming a polymer layer which interferedwith subsequent polycide etching. C₂ F₆ evidently produces a polymerwithout this affinity for tungsten silicide, thereby eliminatingmicromasking.

The inventive process includes a high pressure atmosphere in order toproduce a faster oxide etch rate. High pressure results in a higherfluorine radical flux on the oxide surface. When combined with high rfpower, the etch rate is increased. High pressure and rf power do havedrawbacks, however. Although rf induced ion bombardment assists in oxideetch, it also contributes to photoresist erosion, which is undesirable.Further, if rf power is too high, the resist will "burn" or reticulate.Higher pressure makes a thicker atmosphere, scattering ions and gasradicals in the plasma, resulting in more sidewall etching than with alow pressure system.

The oxide etch step of the inventive method includes an overetch ofabout 45 seconds to fully clear all residual oxide. Although the C₂ F₆/CF₄ /CHF₃ gas mixture etches underlying polycide during overetch, theetch continues to be anisotropic because of the sidewall passivationprovided by the halocarbon-derived polymer and from the carbonintroduced by eroding resist. After oxide has been cleared, thepolycide-to-resist etch rate ratio is approximately 1.8:1.

Polycide etch step details are now provided. Although preferredparameter values have been stated, plasma power density can range withinabout 0.18-2.0 W/cm², the gap can vary within about 0.5-2.5 cm, 0.8-1.5cm being the preferred range, and the pressure can range within about0.200-0.550 torr, although about 0.300-0.425 torr is preferred.Quantities of the gases may vary, as long as at least about 50 sccm Heis provided. It is contemplated that SiCl₄ or BCl₃ or a combinationthereof might be used to provide additional Cl₂, if desired.

The lower pressure of the polycide etch allows for more ion bombardment,which, with resist erosion and the Cl₂ concentration, determines theetch rate and profile of the silicide and poly layers 12 and 13. Cl₂provides the necessary selectivity to the polycide, so that minimalunderlying gate oxide 14 is etched. Fluorine can also be used, but Cl₂is preferred because it provides superior selectivity. The resist usedmust therefore be able to reasonably withstand a chlorine based plasma.The preferred embodiment utilizes Hunt's 6512 resist, developed withHunt's photoresist developer 428. It is realized that other resists,developers, and mask layer compositions can be used as well.

An additional benefit of the inventive method is the ability to usecarbon generated by the resist to help passivate polycide sidewalls,which means that carbon-containing gases do not have to be added to thegas mixture during polycide etch.

There is an upper rf power limit that can be safely used before thepoly-to-gate oxide selectivity is reduced to the point where the polycannot be completely etched without removing all of the exposed gateoxide. The inventive process provides a selectivity of approximately13:1. Variations in the chlorine flow and total pressure do notsignificantly change this selectivity, although an increase in rf powerreduces it.

In both of the inventive steps, helium is added to improve etchuniformity. The pressure, power, and various gas quantities are balancedto produce the fastest etch rates while preserving selectivity.

Clearly, in view of the above disclosure, other embodiments of thisinvention will present themselves to those of ordinary skill insemiconductor processing, such as applying the invention to other kindsof masking layers, oxide, silicide, such as commonly referred to astungsten silicide, tantalum silicide, molybdenum silicide, and titaniumsilicide, and poly, and varying thickness and doping of each layeretched. Since the inventive process includes one step for polycide etch,a simple oxide/poly structure can be etched instead of anoxide/silicide/poly structure, without materially altering the process.It is also conceivable that plasma power density and gap may be varied,gas quantities adjusted, similar gases substituted, or some other inertmaterial used for the cathode, to achieve same or similar results. Gasquantities may also be changed while preserving essentially similarratios of one gas to another. Another make of reactor might also bechosen. These variations and others are intended to be circumscribed bythese claims.

I claim:
 1. A method to anisotropically etch a structure including asilicide on a layer of polycrystalline silicon on a substrate formed asa wafer, said etch performed by a plasma generated by the application ofpower to a gas forming a portion of an atmosphere in a reactor, saidmethod comprising the steps of:a) providing a parallel plate plasma etchreactor as said reactor, said parallel plate plasma etch reactor havinga first electrode and having a second electrode that is non-erodible bysaid plasma generated in said gas in said reactor; b) transferring saidsubstrate into said parallel plate plasma etch reactor upon said firstelectrode located therein, c) introducing a first atmosphere of said gasinto said parallel plate plasma etch reactor, said first atmospherecomprising predominantl C₂ F₆ gas: d) generating a first plasma usingsaid predominantly C₂ F₆ gas as said first atmosphere in said parallelplate plasma etch reactor by the application of said power thereto; e)etching said silicide in said parallel plate plasma etch reactor usingsaid first plasma of said first atmosphere comprising C₂ F₆ as thepredominant gas forming said first atmosphere in said parallel plateplasma etch reactor, thereby forming a plasma having a quantity ofCF_(x) species formed therein and having relatively few fluorineradicals formed therein as compared with the quantity of said CF_(x)species, thereby, in turn, reducing micromasking from carbon depositingon said wafer, by achieving etching selectively without proportionallyincreasing polymer buildup, thereby, in turn, reducing areas of saidsilicide on said layer of polycrystalline silicon which are not etched;f) introducing a second atmosphere within said parallel plate plasmareactor prior to removing said wafer therefrom, said second atmospherecomprising: constituents of Cl₂ ; an inert carrier gas, said inertcarrier gas of said second atmosphere including at least 50 sccm Hetherein; g) generating a second plasma using said second atmosphereintroduced in said parallel plate plasma etch reactor by the applicationof said power thereto; and h) exposing said structure to said secondplasma in said second atmosphere thereby causing further etching of saidstructure.
 2. The method of claim 1, wherein,a) said second atmospherehas a pressure of at least 0.325 torr and includes at least 90 sccm Cl₂,and at least 70 sccm He as said inert carrier gas; b) a power density ofsaid second plasma in said second atmosphere is at least 0.57 W/cm² ; c)a gap of at least 1.0 cm exists between said first and second electrodesin said second atmosphere; and d) said non-erodible second electrodecomprises anodized aluminum.
 3. The method of claim 1, wherein:a) saidsecond atmosphere has a pressure in the range of 0.200 to 0.550 torr; b)a power density of said second plasma in said second atmosphere is inthe range of 0.18 to 2.0 W/cm² ; c) a gap in the range of 0.5 to 2.5 cmexists between said first and second electrodes in said secondatmosphere; and d) said non-erodible second electrode comprises anodizedaluminum.
 4. The method of claim 1, wherein:a) said second atmospherehas a pressure in the range of 0.300 to 0.425 torr; b) a power densityof said second plasma in said second atmosphere is in the range of 0.18to 2.0 W/cm² ; c) a gap in the range of 0.8 to 1.5 cm exists betweensaid first and second electrodes in said second atmosphere; and d) saidnon-erodible second electrode comprises anodized aluminum.
 5. The methodof claim 1, wherein said second atmosphere includes at leastapproximately 50 sccm He.
 6. The method of claim 1, wherein said layeris masked with a mask layer that releases a carbon compound as said masklayer erodes.
 7. The method of claim 1, wherein said silicide comprisestungsten silicide.
 8. A method to anisotropically etch a structureincluding tungsten silicide on a layer of polycrystalline silicon on asubstrate formed as a wafer, said etch performed by a plasma generatedby the application of power to a gas forming a portion of an atmospherein a reactor, comprising the steps of:a) masking said layer with a masklayer that erodes; b) providing a parallel plate plasma etch reactor assaid reactor, said parallel plate plasma etch reactor having a firstelectrode and having a second electrode that is non-erodible by saidplasma; c) transferring said substrate into said parallel plate plasmaetch reactor upon said first electrode located therein; d) providing anatmosphere within said parallel plate plasma etch reactor, saidatmosphere comprising:a gas having primary constituents of Cl₂ and aninert carrier gas, said atmosphere having a pressure within saidparallel plate plasma etch reactor in the range of 0.200 to 0.550 torr;e) generating a plasma by the application of said power to said gas insaid parallel plate plasma etch reactor in the range of 0.18 to 2.0W/cm² : and f) exposing said structure to said plasma generated by theapplication of said power to said gas in said parallel plate plasma etchreactor in the range of 0.18 to 2.0 W/cm², thereby etching said tungstensilicide.
 9. The method of claim 8, wherein:a) a gap in the range of 0.3to 0.6 cm exists between said first and second electrodes; and b) saidnon-erodible second electrode comprises anodized aluminum.
 10. Themethod of claim 8, wherein said atmosphere includes at least 5 sccm Heas said inert carrier gas.
 11. A method to anisotropically etch astructure including a silicide one layer of polycrystalline silicon on asubstrate formed as a wafer, said etch performed by a plasma generatedby the application of power to a gas forming a portion of an atmospherein a reactor, comprising the steps of:a) providing a parallel plateplasma etch reactor as said reactor, said reactor having a firstelectrode and having a second electrode that is non-erodible by saidplasma generated in said reactor; b) transferring said substrate formedas a wafer upon said first electrode of said parallel plate plasma etchreactor; c) introducing a first atmosphere of said gas into saidparallel plate plasma etch reactor comprising predominantly C₂ F₆ gas;d) generating a first plasma using said predominantly C₂ C₆ gas as saidfirst atmosphere in said parallel plate plasma etch reactor by theapplication of said power thereto; e) etching said silicide in saidparallel plate plasma etch reactor using said first plasma of said firstatmosphere comprising C₂ F₆ as the predominant gas forming said firstatmosphere in said parallel plate plasma etch reactor, thereby providinga plasma having a quantity of CF_(x) species formed therein and havingrelatively few fluorine radicals formed therein as compared with thequantity of said CF_(x) species, thereby in turn, reducing micromaskingfrom carbon depositing on said wafer, by achieving etching selectivelywithout proportionally increasing polymer buildup, thereby, in turn,reducing areas of said silicide on said layer of polycrystalline siliconwhich are not etched; f) introducing a second atmosphere within saidparallel plate plasma reactor prior to removing said wafer therefrom,said second atmosphere comprising: constituents of Cl₂ and an inertcarrier gas, said inert gas carrier including at least 50 sccm Hetherein; g) generating a second plasma using said second atmosphere insaid parallel plate plasma etch reactor by the application of said powerthereto; and h) exposing said structure to said second plasma in saidsecond atmosphere, wherein: said second atmosphere has a pressure in therange of 0.200 to 0.550 torr; a power density of said second plasma insaid second atmosphere is in the range of 0.18 to 2.0 W/cm² ; a gap inthe range of 0.5 to 2.5 cm exists between said first and secondelectrodes of said parallel plate plasma etch reactor in said secondatmosphere introduced therein; and said non-erodible second electrode ofsaid parallel plate plasma etch reactor comprises anodized aluminum. 12.The method of claim 11, wherein:a) said second atmosphere has a pressurein the range of 0.300 to 0.425 torr; b) a power density of said secondplasma is said second atmosphere is in the range of 0.18 to 2.0 W/cm₂ c)a gap in the range of 0.8 to 1.5 cm exists between said first and secondelectrodes in said second atmosphere; and d) said non-erodible secondelectrode comprises anodized aluminum.
 13. The method of claim 11,wherein the layer is masked with a mask layer that releases a carboncompound as it erodes.
 14. The method of claim 11, wherein the metalsilicide is tungsten silicide.
 15. A method of anisotropically etching astructure including a layer of silicide and a layer of polycrystallinesilicon on a substrate formed as a wafer, said etch performed by aplasma generated by the application of power to a gas forming a portionof an atmosphere in a reactor, comprising the steps of:a) masking saidsilicide layer with a mask layer that erodes; b) providing a parallelplate plasma etch reactor as said reactor, said parallel plate plasmaetch reactor having a first electrode and having a second electrode thatis non-erodible by said plasma; c) transferring said substrate into saidparallel plate plasma etch reactor upon said first electrode locatedtherein; d) providing an atmosphere within said parallel plate plasmaetch reactor, said atmosphere comprising:a gas having primaryconstituents of Cl₂ and an inert carrier gas; e) generating a plasma bythe application of said power to said gas in said parallel plate plasmaetch reactor; and f) exposing said structure to said plasma in generatedby the application of said power to said gas in said parallel plateplasma etch reactor thereby etching said layer of silicide.
 16. Themethod of claim 15, wherein:a) a gap in the range of 0.3 to 0.6 cmexists between said first and second electrodes; and b) saidnon-erodible second electrode comprises anodized aluminum.
 17. Themethod of claim 15, wherein said atmosphere includes at least 5 sccm Heas said inert carrier gas.
 18. A method of anisotropically etching astructure including a layer of silicide and a layer of polycrystallinesilicon on a substrate formed as a wafer, said etch performed by aplasma generated by the application of power to a gas forming a portionof an atmosphere in a reactor, comprising the steps of:a) masking saidsilicide layer with a mask layer that erodes; b) providing a parallelplate plasma etch reactor as said reactor, said parallel plate plasmaetch reactor having a first electrode and having a second electrode thatis non-erodible by plasma; c) transferring said substrate into saidparallel plate plasma etch reactor upon said first electrode locatedtherein; d) providing an atmosphere within said parallel plate plasmaetch reactor, said atmosphere comprising:a gas having primaryconstituents of Cl₂ and an inert carrier gas, said atmosphere having apressure within said parallel plate plasma etch reactor in the range of0.200 to 0.550 torr; e) generating a plasma by the application of saidpower to said gas in said parallel plate plasma etch reactor in therange of 0.18 to 2.0 W/cm² ; and f) exposing said structure to saidplasma in generated by the application of said power to said gas in saidparallel plate plasma etch reactor in the range of 0.18 to 2.0 W/cm²,thereby etching said layer of silicide.
 19. The method of claim 18,wherein:a) a gap in the range of 0.3 to 0.6 cm exists between said firstand second electrodes; and b) said non-erodible second electrodecomprises anodized aluminum.
 20. The method of claim 18, wherein saidatmosphere includes at least 5 sccm He as said inert carrier gas.
 21. Amethod of anisotropically etching a structure including a silicide on alayer of polycrystalline silicon on a substrate formed as a wafer, saidetch performed by a plasma generated by the application of power to agas forming a portion of an atmosphere in a reactor, comprising thesteps of:a) providing a parallel plate plasma etch reactor as saidreactor, said reactor having a first electrode and having a secondelectrode that is non-erodible by said plasma generated in said reactor;b) transferring said substrate formed as a wafer upon said firstelectrode of said parallel plate plasma etch reactor; c) introducing afirst atmosphere of said gas into said parallel plate plasma etchreactor comprising predominantly C₂ F₆ gas; d) generating a first plasmausing said predominantly C₂ F₆ gas as said first atmosphere in saidparallel plate plasma etch reactor by the application of said powerthereto; e) etching said silicide in said parallel plate plasma etchreactor using said first plasma of said first atmosphere comprising C₂F₆ as the predominant gas forming said first atmosphere in said parallelplate plasma etch reactor thereby selectively etching of said substrate;f) introducing a second atmosphere within said parallel plate plasmareactor prior to removing said wafer therefrom, said second atmospherecomprising:constituents of Cl₂ and an inert carrier gas, said inert gascarrier including He therein; g) generating a second plasma using saidsecond atmosphere in said parallel plate plasma etch reactor by theapplication of said power thereto; and h) exposing said structure tosaid second plasma in said second atmosphere, wherein:said secondatmosphere has a pressure in the range of 0.200 to 0.550 torr; a powerdensity of said second plasma in said second atmosphere is in the rangeof 0.18 to 2.0 W/cm² ; a gap in the range of 0.5 to 2.5 cm existsbetween said first and second electrodes of said parallel plate plasmaetch reactor in said second atmosphere introduced therein; and saidnon-erodible second electrode of said parallel plate plasma etch reactorcomprises anodized aluminum.
 22. The method of claim 21, wherein:a) saidsecond atmosphere has a pressure in the range of 0.300 to 0.425 torr; b)a power density of said second plasma in said second atmosphere is inthe range of 0.18 to 2.0 W/cm₂ c) a gap in the range of 0.8 to 1.5 cmexists between said first and second electrodes in said secondatmosphere; and d) said non-erodible second electrode comprises anodizedaluminum.